Containers for handling thin liquids have generally been provided with one cap or stopper for sealing the liquid in the container and a separate pouring spout which is substituted for the stopper when it is desired to pour the liquid from the container. This is particularly true in containers which store volatile liquid fuels, such as camping stove gasoline. Frequently, particularly for backpacking stove liquid fuel bottles, the pouring spout is tied with a piece of string to the stopper to avoid being lost. The necessity of having two pieces, one which must be completely substituted for the other, is an inconvenience and added expense.
It is important that no trapped or residual quantities of volatile liquid be able to leak out of the stopper or the spout when the fuel bottle is placed into a backpack or other storage location. Even a fraction of a teaspoon of the fuel, if it leaks into the backpack, will create unpleasant odors and perhaps an unsafe condition.
Various types of combined pouring spouts and stoppers for liquid storage bottles are described in patent literature. U.S. Pat. No. 3,067,916 discloses a one-piece cap. This one-piece cap, however, does not adequately seal against leakage of liquid and requires a specially designed bottle for its use. Furthermore, if volatile liquid is being poured, the cap shown in this patent will trap quantities of the volatile liquid which will be free to leak out of the cap at a later period.
Other types of caps have been designed for dispensing of thick liquids. A typical dispensing cap is shown in U.S. Pat. No. 4,065,037. This type of cap, however, frequently is not provided with vent openings and has numerous locations for trapping liquids. Furthermore, since only thick liquids are being dispensed, there are frequently inadequate seals provided around the threads, making them unusable for thin liquids.
Other types of caps are typified by U.S. Pat. No. 3,776,433. This type of cap is primarily used for pouring coffee or other hot, thin liquids into a wide-mouthed container, such as a coffee mug. One difficulty with this type of cap, if used for more volatile fluids, is that the threads are sealed internally so that no liquid can reach the threads. This is undesirable for plastic parts as these threads will bind, particularly if both threaded parts are of plastic. Furthermore, the sealing to prevent leakage out of the bottle is simply two plastic surfaces, which is not adequate for thin liquids and is particularly undesirable for volatile thin liquids.